This invention relates generally to stepping motor control systems and in particular to a control system for obtaining non-oscillatory single step operation of a stepping motor.
Stepping motors are generally used to move some form of apparatus from one position to another position with a high degree of accuracy. Stepping motors are designed with a number of null positions, e.g., 200 null positions for a single rotation of the motor's rotor. In a preferred mode of operation, when the rotor is to be advanced to the next null position, the advancement should take place quickly and without an undershoot and/or overshoot so as to facilitate the positioning of the driven apparatus in the quickest possible manner. Generally speaking, the rotor tends to overshoot the null position and to then reverse direction back towards the desired null position and to continue this oscillatory behavior for a period of time, which in turn decreases the accuracy of the positioning of the rotor to the null position while increasing the settling time of the rotor in its new null position.
The aforementioned problem has been recognized and attacked by prior art controllers. A representation of the state of the prior art, directed towards a solution of the above problem, is set forth in the teachings of the following listed patents:
U.S. Pat. No. 4,490,665 entitled, "Method For Driving A Stepper Motor" by R. C. Meyer; PA0 U.S. Pat. No. 4,564,796 entitled, "Driving Circuit For A Stepping Motor" by T. Yoshimo et al.; and PA0 U.S. Pat. No. 3,573,592 entitled, "Single Step Stepping Motor Control" by G. J. Agin.
In U.S. Pat. No. 4,490,665, the stepper motor is accelerated quickly by applying a high level drive voltage during the initial stepping phase of motor operation and therafter reducing the high voltage to a normal standby or low voltage. In U.S. Pat. No. 4,564,796, a driving circuit drives the stepping motor in a two-phase operation and switches to a single-phase operation immediately before stopping the motor, thereby achieving a degree of stability in the stopped position. In U.S. Pat. No. 3,573,592, the stepping motor is driven in the usual manner with drive triggers to start the step operation and upon nearing the null position gating circuitry is used to obtain a one step-backward function for terminating the single step operation.